Adjustable impedance matching transformers



Aug. 2, 1966 c. EDWARD$ ADJUSTABLE IMPEDANCE MATCHING TRANSFORMERS FiledNov. 15, 1961 4 Sheets-Sheet 1 FIG. IA

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A TTOR/VE V Aug. 2, 1966 C F. EDWARDS ADJUSTABLE IMPEDANCE MATCHINGTRANSFORMERS Filed Nov. 15, 1961 4 Sheets-Sheet 2 m/ VEA/ TOR C. EEDWARDS A T TOR/V5 V 966 c. F. EDWARDS 3,2645% ADJUSTABLE IMPEDANCEMATCHING TRANSFORMERS Filed Nov. 15, 1961 4 Sheets-Sheet 5 nvvavroe ByCFEDWARDS W daww A T TORNEV 2, 1966 c. F. EDWARDS 3,264,584

ADJUSTABLE IMPEDANCE MATCHING TRANSFORMERS Filed Nov. 15, 1961 I 4Sheets-Sheet 4 A TTORNE V United States Patent 3,264,584 ADJUSTABLEIMPEDANCE MATCHING TRANSFORMERS Charles F. Edwards, Red Bank, N.J.,assignor to Bell Telephone Laboratories, Incorporated, New York,

N.Y., a corporation of New York Filed Nov. 15, 1961, Ser. No. 152,534 14Claims. ((11. 33333) This invention relates to electrical networks andmore particularly to adjustable impedance matching transformers.

Generally, radio frequency transmission systems are composed of manyseparate component parts connected by a number of low-loss transmissionlines. In such systems the impedance of each of the component parts ispreferably made equal to the characteristic impedance of thetransmission line connecting the parts. There are several reasons formatching impedances in arbitrary systems, the primary one being thatmaximum energy is transferred from one component to another when theirimpedances are matched; moreover, a matched condition eliminatesreflected wave energy and minimizes the losses in the transmission line.

Typically, components of high frequency transmission systems intended totransmit or utilize wave energy are matched to the interconnectingtransmission lines by means of reactive impedance matching networks.Such networks can be lengths of transmission line utilizing tuned stubsor dielectric elements. The behavior of such matching networks issubstantially equivalent to the more conventional circuits used at lowerfrequencies.

Typically the matching network is an integrated structure which isinserted between two components to be matched or between a component anda transmission line.

For laboratory and test use it is desirable that these impedancetransformers be variable, so that a simple manual adjustment enables theoperator to match any two impedances. Transformers of the single, doubleand triple-stub variety have been used extensively for this purpose butthey suffer from certain drawbacks, one of which is the fact that atleast two manual adjustments must be made in order to match any twoimpedances.

In many instances, especially those encountered in laboratory practice,it is desirable to match impedances which are purely resistive. Whenusing one of the prior art variable impedance transformers for thispurpose, it is still necessary to make at least two manual adjustmentsin order to eliminate any re-act-ance introduced by the transformeritself. By a novel arrangement of reactive elements, the presentinvention obviates this necessity.

It is, therefore, the general object of the present invention to providea matched coupling between networks of diverse impedances.

It is a more specific object of the present invention to providetransformers for matching purely resistive impedances and capable ofbeing adjusted by a single manual control.

It is yet another object of the present invention to provide impedancematching transformers wherein the reactive and resistive components canbe adjusted separately.

In keeping with the principles of the present invention the foregoingobjects are accomplished through the use of T and 1r networks comprisingadjustable reactance elements. In the high frequency embodiments of theinvention, open and shorted coaxial line stubs are utilized as thenetwork elements, whereas in the low frequency embodiments inductors andcapacitors are utilized as the network elements.

As mentioned above, a feature of the present invention is the mechanicalcoupling between the elements of "ice the impedance matching transformerwhich allows the tuning to be done with one manual adjustment. In onespecific embodiment of the invention the impedance matching ratio isadjusted by varying the reactances of a plurality of coupledopen-circuited and short-circuited coaxial line sections. In accordancewith the principles of the present invention the react-ances are variedsimultaneously and in such a manner that the reactances of two of thesections are always maintained equal to each other and the reactance ofthe third section is maintained equal to the negative of the other two.

In an illustrative embodiment of the invention, the mechanic-a1 meansfor performing this adjustment comprises a rack and pinion geararrangement mounted on the transformer structure. In the low frequencyembodiments of the invention the impedance matching ratio of thetransformer is adjusted by varying either the capacitances or theinductances of the various network elements simultaneously. In theseembodiments the me chanical means is easily integrated into thecapacitor or inductor structure in the form of ganged capacitors andinductors.

The above mentioned and other features and objects of this inventionwill become more apparent by reference to the following descriptiontaken in conjunction with the accompanying drawings in which:

'FIGS. 1A and 1B are simplified circuit diagrams of T and 1: networksfor facilitating the description of the invention;

FIGS. 2A and 2B are schematic representations of open and shortedtransmission lines showing the impedances associated therewith;

FIGS. 3A, 3B, 3C, and 3D are cross-sectional views of four highfrequency embodiments of the present invention;

FIG. 4 is a pictorial view, partially in cross section, of a preferredembodiment of the invention;

FIG. 5 is a pictorial view of the embodiment of FIG. 4 illustrating themechanical ganging of the tuning controls;

FIG. 6 is a longitudinal cross-sectional view of a triple stub coaxialimpedance transformer used as an aid in explaining the means by whichprinciples of the present invention may be applied thereto;

FIG. 7A is a schematic representation of a low frequency embodiment inaccordance with the principles of the present invention;

FIG. 7B is a pictorial view of a possible capacitor capable of beingutilized in the embodiment of FIG. 7A; and

FIG. 8 is a schematic representation of yet another low frequencyembodiment in keeping with the principles of the present invention.

Referring to the circuit of FIG. 1A, there is shown a T-networkconsisting of reactive elements X X and X to which there is coupled aload impedance Z The impedance Z of the circuit at terminals 1-1' isgiven by the equation 1 Z 1/ z. +721.) +1/1'X2 (1) By making X 1:X2,Equation 1 becomes +j XrXa and if the T is made symmetrical by making X=X then Similarly, in the 1r-network of FIG. 1B, if the reactiveelements B B and B are adjusted so that the equation for theadmittanceas seen across terminals 1-1' is Equations 3 and 4 are similarin form to the input im pedance and admittance of quarter-wave sectionsof transmission line terminated with loads Z and Y respectively. Theseequations are where Z and Y are the characteristic impedance and thecharacteristic admittance of the lines.

In other words, the networks of FIGS. 1A and,

1B, when properly adjusted, behave electrically as quarter-wavetransmission line sections and enjoy the same impedance transformingproperties. The important distinction between an actual quarter-wavetransmission line and a so-called artificial transmission line ofFIG.'1A'

or 1B is-that the characteristic impedance ofthe artificial transmissionline can'be easily varied whereas the characteristic impedance of a realline can not. And even if, with some difliculty, the impedance of a realline can be varied, the range of variation is quite limited.

If, however, sections of transmission line are connected together andtheir, lengths proportioned in the manner to be explained in detailhereinbelow, the disadvantages peculiar to the individual transmissionline when used as a quarter-wave matching section no longer exist. Inaccordance with the invention the several lengths of trans mission lineserve, not as impedance transformers, but as reactance elements in a Tor 1r network.

FIG. 2A shows an open-circuited transmission line section of length xhaving a characteristic impedance Z In practice, the resistive losses ofa short line can be neglectedand when this is done the impedance lookinginto terminals 11 is a pure reactance given by:

where the phase constantfl equals 21r/7\, and A is the It viewedfromtthe wavelength in the transmission line. admittance standpoint, thesusceptance B at terminals 1-1' is given by:

Z0 tan 6a:

FIG; 2B shows a section of transmission line of length.

l and characteristic impedance Z short-circuited atone of its ends.Again, if the resistive losses are neglected the impedance looking intoterminals 22' is a pure re-- I actance If the lengths of the two linesare made adjustable so that the sum of their lengths x+l is'equal to M4,the reactance of the open-circuited section can be written as V, Z m

4% Substituting for x,

E e l/Z tan p( \/4+ l)-=1/Z tan (1r/2,8l)

and since tan .(1r/2iA)=cot A,l.then;

hi I B Z0 cot. til

It is apparent .from Equations. 5 throughw8 that X =X and B =BThese,'however,.are the requirements thatmust be met by X and X2 and Band 'B iinthe networksof FIGSylA and lBiinzorder to obtainimpedancettrans-formingt action, Thus, by combin-l ing anopen and ashorted transmission line section, :the-

sum of whoselengths is a ;qu arter.wavelength, and by adding anotheropentor, shorted transmission, line sec-l tion as the third reactiveelement, ;various circuits having the desired impedance, transformingproperties are'hobtained. Furthermore, if the reactance of the varioussections is changed by varying ;their:lengths, the circuits are capableof providing, a wide range of impedance-ratios. FIGS.- 3A and-=3B arecross-sectionalvieWs of two:

embodiments of the invention utilizing coaxial line constructionarranged in the manner of a T-network. FIG"; 3A shows a thigh-passT-network consisting of substan-t -tially identical quarter-Wavelengthinner; conducting rods 10 and 11 joined by conductor 12 which makesa;slideable contact with each along their, respective lengths;

The regions, of rods 10 and 11 below the'slideable'junc-l tionprovidecltby conductor lz are surrounded by. cylindrical !Olltlconductors 13 and 14, respectively. The

regions ofrods 10iand 11 above these-points are surrounded bycylindrical condu'cting sheaths 15 and '16 which, in turn; aresurrounded by cylindrical outer con-= Inner conducting rods: 10 land :11are shorted ,tozouter- V conductors l3 and -l4 byv means ofshortingdisks 19 and 20. This construction enables rods 101and 11 to move inadirection-parallel to vtheir longitudinal faxes while maintaining:contact with outer HCOHdUCtOISe 13, and 14. The dashed line connectingrods 10 andvll indicates a mecihanical connection for, moving botharodsi simultaneous y.

Input connections to the device are provided across the open ends'ofouter conductor 17 and sheath'15. The

load lmpedance Z, to be transformed is connected across 1 outerconductor '18 and sheath ;16.- The input: and

output connections can, of course, be interchanged as seen from thesymmetry of the device.

Returning to the terminology of FIG. 1A," it is evident that the coaxialsection formed by rod 11 and sheath 16 corresponds to the reactance Xi,and the coaxial section formed by rod 10 and sheath 15 corresponds toreactantce X5. The parallel. combination of the two ,sec-

tions formediby .rods 10 and Hand outer conductors 13 and 14,respectively, corresponds to the third reactance X 7 In'operation, theimpedance transforming ratio is changed when rods 10 and 11 are movedsimultaneously in a direction parallel to their From the vstandpoint ofsymmetry,-i=t is seen that X land X3 are always equal; and since the:lengths of rods 10 and 111 are onequarter wavelength at a the operatingfrequency,

In FIG. 33, there is shown a lowepass T-network substantially identicalto the high-pass network of FIG. 3A. In this figure like numerals havebeen utilized to indicate the correspondences, between the elements 201.this embodiment and that of FIG. 3A. The only substantial differencebetween this embodiment and the previous one is that shorting disks 19'and 20 have replaced disks 19 and 20, respectively. The functions of thevarious elements and combinations of elements are substantially the sameas those of FIG. 3A except that rods and 11 are now shorted toconducting sheaths 15 and 16.

In keeping with the principles of the present invention, the coaxialline sections formed by rods 10 and 11 and sheaths 15 and 16; andsheaths 15 and 16 and outer conductors 17 and 18 are designed so thattheir characteristic impedances are equal. Since the coaxial sectionsformed by rods 10 and 11 and outer conductors 13 and 14 are in(parallel, they are :designed to have a characteristic impedance equalto twice this value.

In FIG. 3C there is shown in cross section another embodiment of thepresent invention intended tfor operation at high radio frequencies.This embodiment is a coaxial Ir-IlfifiWOlk arranged in the manner of ahighpass filter. In this embodiment two substantially identicalquarter-wavelength conducting rods 21 and 22 are slideably connectedalong their lengths to conductors 30 and 31, respectively. Conductors 30and 31, in turn, serve as the inner conductors of the input and outputcoaxial line sections 34 and 35, respectively. Rods 21 and 22 aresurrounded by outer conductors 23 and 24 over that portion of theirlengths below the points of connection with conductors 30 and 31. Theregions of rods 21 and 22 lying above these points extend into twocylindrical cavities 25 and 26, respectively, which have been fiormed ina solid conducting element 27.

Element 27, which is proportioned so that its length is equal toone-quarter wavelength at the operating frequency, is, in turn,surrounded by an outer conductor 28 and conductively attached thereto byend-plate 29. The coaxial input and output sections as well as outerconductors 23, 24, and 28 are oonductively joined so as to provide ashield surrounding rods 21 and 22 and conductors 30 and 31.

Shorting disks 32 and 33 are attached to the lower end points of rods 21and 22, respectively, so that each rod is slideably shorted to itscorresponding outer condoctor 23 and 24. Again, for the sake of clarity,the means for positioning and holding conductors 30 and 31 have not beenshown but can comprise any of the lowloss dielectric beads or spacersknown in the art.

In the terminology set forth in connection with FIG. 1B, the coaxialsection formed by nod 22 and outer conduotor 24 corresponds to thesusceptance B The coaxial section formed by rod 21 and outer conductor23 corresponds to susceptance B and the series combination of thecoaxial sections formed by rod 21 and cavity 25 and rod 22 and cavity 26corresponds to the third susceptance B Again, it is obvious from thesymmetry of the structure that B and B are always equal; and since thelengths of rods 21 and 22 are one-quarter wavelength at the operatingfrequency, B =B In FIG. 3D, there is shown another embodiment of thepresent invention substantially identical to that of FIG. 30, whereinthe numbering of the elements has been carried over from thecorresponding elements of that embodiment. This embodiment i a low-passIr-network wherein the shorting disks 32' and 33' have replaced disks 32and 33 so that rods 21 and 22 are slideably shorted to the innerconducting surfiace of cylindrical cavities 25 and 26, respectively.

In operation, rods 21 and 22 in both embodiments 3C and 3D are movedsimultaneously along their longitudinal axes. The mechanical means foroperating this portion is not shown but merely indicated by the dashedline.

In the embodiments of FIGS. 3C and 3D the coaxial line sections formedby rods 21 and 22 inside outer conductors 23 and 24 are designed to havea given characteristic impedance, and since the coaxial sections formedby rods 21 and 22 inside cavities 25 and 26 are in series, thesesections are designed to have a characteristic impedance of one-halfthis value. As mentioned above, the coaxial line section formed byelement 27 and outer conductor 28 is one-quarter Wavelength long;therefore, it has no effect on the other coaxial sections and itscharacteristic impedance is not critical.

In FIG. 4 there is shown, partially in cross section, a refinement ofthe present invention derived from the embodiment of FIG. 3C. Thisembodiment consists of hollow, cylindrical conductors 40 and 41 ofsubstantially equal cross-sectional dimensions oriented so that theirends are in close proximity and their axes colinear. A conducting rod 42extends along this common axis through conductor 41 and into conductor40.

Rod 42 is conductively insulated from conductor 40 by dielectric disk 43which allows longitudinal motion of rod 42 relative to conductor 40'.Rod 42 is joined to inner conductor 44 of coaxial transmission linesection 45 by means of a spring contact 46. Contact 46 is located in theregion between conductors 40 and 41. The nature of contact 46 is suchthat it allows rod 42 to move longitudinally while maintainingelectrical contact with inner conductor 44.

Cylindrical conductor 40 is conductively connected to inner conductor 47of coaxial line transmission section 48 at its end nearest conductor 41.Connection 49 is a rigid one and allows no relative motion betweenconductors 40 and 47.

Conductor 40, which surrounds a portion of rod 42, is, in turn,surrounded by a cylindrical outer conductor 50. Conductor 50 extends theentire length of conductor 40 and is joined to conductor 41 and theouter conductors of transmission line sections 45 and 48. In this mannerconductors 41 and 50 and the outer conductors of transmission linesections 45 and 48 form a continuous surface.

Conductors 40 and 50 are conductively shorted by annular shorting ring51. Ring 51 is attached to cylinder 52 which extends past the ends ofconductors 40 and 50 and enables the position of the short provided byring 51 to be adjusted.

Rod 42 is shorted to conductor 41 by means of annular shorting ring 53which is attached by means of rods 54 to another ring 55 lying outsidethe end of conductor 41. Set-screw 56 is provided in ring 55 in order toclamp the two rings 53 and 55 in position on rod 42. Thus, ring 53 canbe moved with respect to rod 42 and conductor 41 or with respect toconductor 41 only.

The lengths of the three coaxial sections which make up the impedancetransformer in the present embodiment have been designated l l andLength 1 is that of the shorted coaxial section formed by conductor 41and rod 42 extending from spring contact 46 to shorting ring 53. Length1 is that of the open-ended coaxial section formed by conductor 40 androd 42 between contact 46 and the end of rod 42. And length 1 is that ofthe shorted coaxial section formed by outer conductor 50 and conductor40 between junction 49 and shorting ring 51. In keeping with theprinciples of the present invention, the three coaxial sections referredto are proportioned so that they all have the same characteristicimpedance Z In operation, 1 and 1 are made equal by adjusting theposition of shorting ring 51 or 53. This adjustment is easily made ifcylinder 52 and either of rods 54 has first been calibrated and thelengths marked thereon. After this preliminary adjustment rod 42 isadjusted so that the length l +l is electrically equal to one-quarterwavelength at the operating frequency. This adjustment is fiacilitatedby observing the impedance at input section 48 when the output section45 is terminated with a purely resistive impedance. When the length l +Zis properly adjusted the impedance seen at the input of the device hasno imaginary component.

In order to operate the device as an adjustable impedance matchingtransformer, it'is' necessaryito vary The other requirement that l +lequal one-quarter vwave-- the lengths so that l and are always equal.

length is metif the shorting ring 5 3 is clamped in place. on rod .42 bymeans of set-screw 56 after its initial adjustment.

FIG. 5 illustrates the mechanical means utilized in adjusting thetransformer of FIG. 4. Like numerals have been employed to designatelike elements in the two figures. A dual rack and pinion arrangementcomprising racks 60 and 62 and pinion gear 64- is mounted on thedeviceas shown. RackGOJisattached to cylinder 52' by means of end plate 61.Similarly, rack62 is attached to ring 55 by means of plate 63. The tworacks are engaged by pinion gear 64 which is manually It is thereforeseen that the range of impedance transformation'can be quite large,depending on the range.

over which l l and 1 can be varied.

It is understood that the mechanical means shown in FIG. 5 is for thepurpose of illustration only and that many other mechanical gaugingarrangements can be utilized in practicing the invention.

The principles of the present invention may also be applied to the priorart device known as the triple-stub tuner. FIG. 6 shows a simplifiedcross-sectional view of such a device. The triple-stub tuner of F'IG.-6comprises a main coaxial transmission line section 70with threeassociated coaxial line stubs'71, 72, and 73,-ar ranged alongthe lengththereof. In general, the longitudinal spacing between consecutive stubsis one-quarter wavelength at the operating frequency. The positions ofthe shorting rings within stubs 71, 72, and 73 are adjustable by meansof cylinders 74, 75, and 76, which may or may not be of conductingmaterial.

The lengths of the input, intermediate, and output stubs have beendesignated l l and I respectively, in order to explain the operation ofthe device of FIG. 6 modifie'd by the principles of the presentinvention. In order to enable the triple-stub tuner to couple a network.of one purely resistive impedance of a given value to that of anotherpurely resistive impedance the following pro- .15 adjusted :by knob 65.The Whole assembly consisting.

cedure should be followed. First, the lengths l and I are maintainedsubstantially equal.

For this purpose 1 cylinders 74 and 76 are rigidly joined by member 77which allows lengths l and 1 to be change-d only simultaneously so that1 always equals 1 Secondly, the lengths l +l (and l +l are made equal toone-quarter wavelength.

The second requirement is met by gauging cylinder .75' '65 Thisarrangement similar to that .of FIGS. Such a mechanism. can be easilyconstructed by a skilled mechanic and is not illustrated in FIG. 6.

So far, the various embodiments of the present invention have only beendescribed with regard to operation wherein one purely resistiveimpedance is transformed i into another purely resistive impedance of adilferent I 811- value; For most laboratory purposes this is the :onlycasethat is encountered. If,ghowever, it is desirable to adjustthe'reactivewomponent of an .impedance so as.

to eliminate it ,in the transformed impedance or; totintroduce areactive component, a furtherstepgcan be, taken.

If it is desired to adjust :the .reactive'component independentlyoftheresistive component, a simple matchresistiveand reactivecontrols can betolerated, this: adjustment can be made without employing a separatestub. In this case, the; real-'or-resistive component can;be adjustedusing the-inventiomas -de'scribed=hereinabove and then by disengagingtheaganging mechanism andadjusting 1 separately to.the desired ,value ofreactance.

The original T and 1r-networks 0f FIGS. 1A and 13 can be exploited toprovide variable impedance transformers for lowerfrequencies. FIGSJ7Aand 8 are schematic diagrams ,oftwo embodiments of the present inventionemploying lumped parameter: circuit elements. FIG 7A is aT-networktuseful in the. .low. megacycle regions; It consists of gangedcapacitors-C C and C and inductor L as the constituent reactiveelements: of 1 thestransforment, The input ofthe transformer'is at ter-'minals v1-1 andthe output is: terminatedby load'im- I pedance R..

Returning to the terminology developed ;in association with FIG. :1A, inFIG. 7A:

C decreases,-then .C +C is maintainedconstantand Equation" 12 issatisfied. The impedanceofthe trans- I former of FIG;:7A, looking intoterminals1-1'=is, from Equations 3 and 12:.

FIG. .7B is asimplified.pictoriajtillustration of a variable capacitorfor use inthe embodiment of FIG. 7A..

The capacitor consists of shafti80aon which there is mounted rotorplates 84, :85, :and 86.; Stator plates 81,

82, and 83 are located .onei-ther side of each of the rotor. plates 84,85, and 86;.respectively. Inthis manner. rotor plate 84 and statorplates 81 form a capacitor 0 plates 82 and 85form capacitor C and plates86 and 83 form capacitor C The. position of stator plates 82 arephysical degrees from the position of p1ates=81*and 83.

Therefore, the capacitance of C 'decreases. as that of C and C increasesand. if the physical dimensions and:

spacing ofeach set of plates are equal,C '|-C is always constant and Cis always equal ,to (3 The present in-: :vention-should not be deemedlimitedby'the capacitor 9 shown in FIG. 7B, since it is included forpurposes of illustration only.

FIG. 8 is a schematic representation of another lowfrequency embodimentof the present invention. The lowpass T-network of FIG. 8 is similar tothe high pass T of FIG. 7A except that inductances L L and L havereplaced C C and C and capacitor C has replaced inductor L. Therequirements in this transformer are that L equal L and L +L or L +L beconstant. If identical tapped inductors are used it is readily seen thatthe above relationships can be satisfied.

In all cases it is understood that the abovedescribed arrangements areillustrative of a small number of the many specific embodiments whichcould represent an application of the principle of the invention. Otherarrangements, including variable impedance transformers utilizingtransmission lines other than the coaxial type can readily be devised inaccordance with these principles by those skilled in the art withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. In combination, a plurality of variable reactances, means forconnecting a first variable reactance X between a first terminal and afirst common junction, means for connecting a second variable reactanceX between said first common junction and a second common junction, meansfor connecting a third variable reactance X between said first commonjunction and a second terminal where X =X X input means connectedbetween said first terminal and said second common junction, outputmeans connected between said second terminal and said second commonjunction, and a single means for adjusting all of said reactancessimultaneously while maintaining the relations X '=X =X 2. Thecombination according to claim 1 wherein said first and third variablereactances are variable capacitors and said second variable reactance isa parallel combination of an inductor and a variable capacitor.

3. The combination according to claim 1 wherein said first and thirdvariable reactances are variable inductors and said second variablereactance is a series combination of a capacitor and a variableinductor.

4. The combination according to claim 1 wherein said first and thirdvariable reactances are open-circuited transmission line stubs and saidsecond variable reactance is at least one short-circuited transmissionline stub.

5. The combination according to claim 1 wherein said first and thirdvariable reactances are short-circuited transmission line stubs and saidsecond variable reactance is at least one open-circuited transmissionline stub.

6. An adjustable impedance matching transformer comprising, incombination, a plurality of variable reactances, means for connecting afirst variable reactance X between a first terminal and a commonjunction, means for connecting a second variable reactance X betweensaid first terminal and a second terminal, means for connecting a thirdvariable reactance X between said second terminal and said commonjunction where X =X X input means connected between said first terminaland said common junction, output means connected between said secondterminal and said common junction, and a single means for adjusting allof said reactances simultaneously while maintaining the relations X =X X7. The combination according to claim 6 wherein said first and thirdvariable reactances are open-circuited transmission line stubs and saidsecond variable reactance is at least one open-circuited transmissionline stub.

8. The combination according to claim 6 wherein said first and thirdvariable reactances are short-circuited transmission line stubs and saidsecond variable reactance is at least one open-circuited transmissionline stub.

9. A variable impedance transformer including, in combination, aplurality of sections of coaxial transmission line all having the samecharacteristic impedance, and connected as follows: a first section ofcoaxial transmission line comprising a hollow inner conductive cylinderand a surrounding outer conductive cylinder; second and third sectionsof coaxial transmission line, each having an inner conductor and asurrounding outer conductor, and each having one end thereof abuttingupon one end of said first line; adjustable means for conductivelyterminating the other end of said first line located at a distance 1from said one end; the outer conductors of said second and third linesmaking conductive contact with the outer cylinder of said first line;means for connecting the inner conductor of said second line to theinner cylinder of said first line at said one end; a fourth section ofcoaxial transmission line having an inner conductor and a surroundingouter conductor colinearly aligned with said first line with the outerconductors thereof in conductive contact; the inner conductor of saidfourth line extending past the inner conductor of said third line andmaking slidable contact therewith and further extending into said hollowinner cylinder a distance past said slidable contact and formingtherewith a fifth section of coaxial transmission line; adjustable meansfor conductively terminating said fourth line at a distance I, from saidslidable contact; means for simultaneously varying said distances l and1 while maintaining the relationships l =l and l +l equal to a constant;and input and output means connected to the other ends of said secondand third lines respectively.

10. An adjustable impedance matching transformer arranged in the mannerof a high-pass T-network comprising a pair of parallel conducting rods,means for conductively connecting said rods at corresponding pointsintermediate the ends thereof, a first pair of hollow cylindricalconductors coaxial to and surrounding a portion of each of said rods andextending from said points past one pair of corresponding ends of saidrods, a second pair of hollow cylindrical conductors coaxial to andsurrounding a portion of each of said rods and extending from saidpoints past the other corresponding ends of said rods, said first andsecond pairs of cylindrical conductors being conductively insulated fromeach other, a third pair of hollow cylindrical conductors coaxial to andsurrounding said second pair of cylindrical conductors over the entirelengths thereof, said first and third pairs of cylindrical conductorsbeing conductively connected, a single mechanical means forsimultaneously varying the position of said points along the lengths ofsaid rods, input means connected between one of said second pair ofcylindrical conductors and the corresponding conductor of said thirdpair of cylindrical conductors, output means connected between the otherof said second pair of cylindrical conductors and the correspondingconductor of said third pair of cylindrical conductors, and means forconductively connecting corresponding ends of said rods to adjacentpoints on the respective conductors of said first pair of cylindricalconductors.

11. An adjustable impedance matching transformer arranged in the mannerof a low-pass T-network comprising a pair of parallel conducting rods,means for conductively connecting said rods at corresponding pointsintermediate the ends thereof, a first pair of hollow cylindricalconductors coaxial to and surrounding a portion of each of said rods andextending from said points past one pair of corresponding ends of saidrods, a second pair of hollow cylindrical conductors coaxial to andsurrounding a portion of each of said rods and extending from saidpoints past the other corresponding ends of said rods, said first andsecond pairs of cylindrical conductors being conductively insulated fromeach other, a third pair of hollow cylindrical conductors coaxial to andsurrounding said second pair of cylindrical conductors over the entirelengths thereof, said first and third pairs of cylindrical conductorsbeing conductively connected, a single mechanical means forsimultaneously varying the position of said points along the lengths ofsaid rods, input means connected between one of said second pair ofcylindrical conductors and the corresponding conductor of said thirdpair of cylindrical conductors, output means connected between the otherof said second pair of cylindrical con-. ductors and the correspondingconductor of said third pair of cylindrical conductors, and means forconductively connectingcorresponding ends of said rods to adjacentpoints on the respective conductors ofv said second pair of cylindricalconductors.

12. An adjustable impedance matching transformerarranged in,the mannerof a high-pass ar-network comprising a pair of parallel conducting rods,means for cone dnctively connecting the inner conductors of a pair ofcoaxial transmission line sections to said rods at corresponding pointsintermediate the ends thereof, a first pair .of hollow cylindricalconductors coaxial to and surroundmeans connectedto one of said coaxialtransmission line 1 sections and output means connected to the other ofsaid coaxial transmission line sections, a single mechanical means forsimultaneously varying the position of said.

points along the lengths of said rods, and means for condnctivelyconnecting corresponding ends of said rods to adjacent points on saidfirst pair of cylindrical conductors.

13. An adjustable impedance matching transformer arranged in the mannerof a low-pass 1r-network comprising a pair of parallel conducting rods,means for conductivelyconnecting the inner conductors of a pairof-coaxial transmission line sections to said rods at correspondingpoints vintermediate the ends thereof, a first pair of hollowcylindrical conductors coaxial to and surrounding a portion of each ofsaid rods and extending from said points past one pair of correspondingends of said rods, the other corresponding endslofasaid,rods-extendingyinto a pair of cylindrical cavities formed in asolid cylindrical conductor, a thirdhollow cylindrical. conductorcoaxial to and surrounding said solid cylindrical conductor over theentire length thereof; said third hollow cylindrical icon-f ductorbeingconductively connected to said solid cylindrical conductor,- to saidfirst pair: of hollow-cylindrical conductors, and .to the outerconductors of, said pair of coaxial transmission line sections, inputmeans connected ,to one of said coaxial t'ran'smission'line sections'andout; put-means; connected to the other of said coaxial transmission linesections, a single mechanical means :for, simul taneously varying theposition of .said vpoints along the lengths of said rods, and meansforconductively connecting corresponding, ends of said rods to adjacentpoints on the inner surface of said=cylindricalzcavities.

14. A triple-stub coaxial line, :tuner comprising, in

combination, a maincoaxial linesection, fir'st,;second,

and third 'short-circuited stubs connected :in shunt with saidmainsection along the-length thereof and spaced one-quater wavelengthapart, said stubs having efiective electrical lengths equal to 1 I and lrespectiv'ely, a single mechanical means foriadjusting all'of saidlengths,

simultaneously while; maintaining the relations 1 :1 and r 'l +l=constant; r

References Cited :by the Examiner UNITED STATES PATENTS 1 2,284,529,5/1942 Mason 3334-33 2,373,233 4/1945 Dow 33333 2,390,839 12/1945Klingaman 33333 2,404,279 7/1946 DOW 333 -33 2,419,985 5/1947 Brown33333 2,422,160' 6/1947 Woodward 333-33 2,428,272 9/1947 Evans 333-732,428,485 10/1947 Carter 333-33 2,438,912 4/1948' Hansen 333-33 HERMANKARI; SAALBACH,Primary Examiner.

C. BARAFF, Assistant Examiner.

1. IN COMBINATION, A PLURALITY OF VARIABLE REACTANCES, MEANS FORCONNECTING A FIRST VARIABLE REACTANCE X1 BETWEEN A FIRST TERMINAL AND AFIRST COMMON JUNCTION, MEANS FOR CONNECTING A SECOND VARIABLE REACTANCEX2 BETWEEN AND FIRST COMMON JUNCTION AND A SECOND JUNCTION, MEANS FORCONNECTING A THIRD VARIABLE REACTANCE X3 BETWEEN SAID FIRST COMMONJUNCTION AND A SECOND TERMINAL WHERE X1=X3=-X2, INPUT MEANS CONNECTEDBETWEEN SAID FIRST TERMINAL AND SAID SECOND COMMON JUNCTION, OUTPUTMEANS CONNECTED BETWEEN SAID SECOND TERMINAL AND SAID SECOND COMMONJUNCTION, AND A SINGLE MEANS FOR ADJUSTING ALL OF SAID REACTANCESSIMULTANEOSULY WHILE MAINTAINING THE RELATION X1=X3=-X2.